(Reuters) - Recreational vehicle shipments in the United States are expected to climb to their highest level in nearly four decades this year, according to an industry association, as millennials join baby boomers in hitting the road.

RV shipments, which include travel trailers and motorhomes, are expected to total 419,500 in 2016, a 12.1 percent jump from a year earlier, and 438,100 in 2017, the Recreation Vehicle Industry Association said on Tuesday.

"The deeply rooted appeal of the RV lifestyle attracted retiring baby boomers as well as first-time buyers..," Richard Curtin, director of the Surveys of Consumers at the University of Michigan, wrote in a study for the association.

The largest unit gains in 2016 and 2017 are expected to be in conventional travel trailers, according to the study.

Sales among millennials are expected to rise as personal income grows, the study said.

Millennials, born in 1980 through 2000, are a growing market, as they prefer to spend on experiences and adventure over material goods, according to data research organization IBIS World.

The U.S economy has regained momentum after stumbling in late 2015 and early 2016 with strength in the labor market bolstering domestic demand.

The economy is on track to grow at a 3.6 percent annualized pace in the fourth quarter after data showed domestic housing starts hit a nine-year high in October.

Quarterly results from RV manufacturers are reflecting the boom in the industry.